Segment Routing (SR) architecture leverages source routing and tunneling paradigms and can be directly applied to an MPLS (Multiprotocol Label Switching) data plane. A node steers a packet through a controlled set of instructions called segments, by prepending the packet with an SR header. Rather than depending on a hop-by-hop signaling technique, SR depends on a set of segments that are advertised by a routing protocol. These segments act as topological sub-paths that can be combined together to form a desired path. Segment Routing allows a head end of the path to impose a stack of labels without knowing the control plane details of each of those labels. This raises challenges in path validation.
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